TM 5-3895-383-2420.Operation at high altitude:The cooling capacity of the cooling system goesdown as the engine is operated at higher altitudes.A system, under pressure, large enough to keepthe coolant from boiling must be used.21.Engine used in a lug condition:"Lugging" can occur when there is too much loadapplied to the engine or the engine is run at a lowerrpm. This low rpm causes a reduction in air flowthrough the radiator, and a reduction in the flow ofcoolant through the system. This combination ofless air and less coolant flow during high input offuel will cause above normal heating.22.Fuel setting:A high fuel setting causes a high heat rejection. Ifthe engine cooling system is designed for aparticular heat rejection and it is changed thecooling system is no longer capable of cooling theengine.23.Fuel injection timing:Check and make necessary adjustments as perTesting and Adjusting Section of the ServiceManual.Problem 27: Below Normal Coolant TemperatureProbable Cause(s):Long Idle PeriodsVery Light LoadsWater Temperature RegulatorAir Vent ValveFan Clutch Engaged1.Long idle periods:When the engine is running with no load, only asmall quantity of fuel is burnt and engine heat isremoved too fast.2.Very light load:Very light loads can cause below normal heatingbecause of the low heat input of the engine. Aslight restriction of air flow through the radiator willhelp to correct this problem.3.Water temperature regulator:A water temperature regulator that is "stuck" open(will not move to the closed position) will causebelow normal heating. A regulator that is stuckbetween the open and closed positions, or a ventvalve that is stuck open, can cause below normalcoolant temperatures when the engine has a lightload.4.Air vent valve:An air vent valve located in the water temperatureregulator that is stuck open, can cause belownormal coolant temperatures when the engine hasa light load.5.Fan clutch engaged:Electric fan clutch engaged. Check temperaturesensor.Problem 28: Exhaust Temperature Is Too HighProbable Cause(s):Air Inlet System Has A LeakExhaust System Has A LeakAir Inlet Or Exhaust System Has A RestrictionIncorrect Fuel Injection Timing DimensionFuel Setting Too HighEngine Operated In A Lug Condition1.Air inlet system has a leak:Check pressure in the air inlet manifold. Look forrestriction at the air cleaner. Correct any leaks.2.Exhaust system has a leak:Find cause of exhaust leak. Make repairs asnecessary.3.Air inlet or exhaust system has a restriction:Remove restriction.4.Incorrect fuel injection timing dimension:Check and make necessary adjustments as perTesting and Adjusting Section of the ServiceManual.5.Fuel setting too high:Check and make necessary adjustments as perTesting and Adjusting Section of the ServiceManual. See Fuel Setting And Related InformationFiche for the correct fuel setting.6-50